(1) Field of the Invention
This invention relates to a processing method for exposed silver halide color photosensitive materials (hereafter) called color photosensitive material), and more particularly to an improved processing method enabling sufficient desilverization to be performed in a short time and high photographic quality to be obtained.
(2) Prior Art
The general basic steps of color photosensitive material processing are the color developing step and the desilverizing step. In the color developing step, the exposed silver halide is reduced by the color developing agent to produce silver, and the oxidized color developing agent reacts on the color coupler to produce a color image. In the next desilverizing step, the silver produced in the color developing step is oxidized by the oxidizing agent (generally called bleaching agent) and the oxidized silver is thereafter dissolved by the complexing agent of silver ions (generally called fixing agent). After the desilverizing step, only the color image remains on the color photosensitive material.
The desilverizing step may be performed by using two baths, a bleaching bath containing the bleaching agent and a fixing bath containing the fixing agent, or by using a single bath, a bleaching-and-fixing bath containing both the bleaching agent and the fixing agent.
In addition to the above basic steps, an actual developing processing includes various auxiliary steps to accomplish several purposes, such as maintaining the photographic and physical qualities of the image and improving the life of the image. For example, the processing may use a hardening bath, a stop bath, an image stabilizing bath, and a washing bath.
The well known bleaching agents are potassium ferricyanite, bichromate, ferric chloride, ferric complex salt aminopolycarboxylate, and persulfate.
Using potassium ferricyanite or the bichromate, however, gives rise to the problem of environmental pollution caused by cyanides or hexavalent chromium. Thus, the use of these agents requires special processing equipment. On the other hand, using the ferric chloride, leads to the problem of the generation of mercurated iron and/or stains in the next washing step. Thus, the use of this agent entails various disadvantages from the point of practical use. Further, persulfate has poor bleaching ability, necessitating a considerably long bleaching time. An improved processing has been suggested for offsetting the disadvantage of persulfate by enhancing its bleaching ability by the use of a bleaching accelerator. Use of the persulfate, however, has another disadvantage in that the persulfate itself is classified as a dangerous material under the Fire Prevention Law, and thus requires various special means for its storage. Therefore, as a practical matter, persulfate is difficult to use.
Ferric complex salt aminopolycarboxylate (especially ferric complex salt ethylenediaminetetraacetate) is the bleaching agent having the most general practical use today since it causes less environmental pollution and fewer storage problems than persulfate. The bleaching ability of ferric complex salt aminopolycarboxylate is, however, not necessarily sufficient. It can be acknowledged that use of ferric complex salt aminopolycarboxylate as the bleaching agent attains the desired objects in the case of performing the bleaching step or the bleaching-and-fixing step for low sensitivity silver halide color photosensitive materials which contain silver chlorobromide emulsion as the main element. However, ferric complex salt aminopolycarboxylate suffers from the disadvantages of poor desilverization ability and long bleaching time when applied to the processing of high sensitivity color photosensitive materials which contain silver chloroiodobromide emulsion or silver bromoiodide emulsion as the main element and also are photochemically sensitized, especially in the case of using the photosensitive materials of high silver emulsion, i.e. photographic color reversal photosensitive materials and photographic color negative photosensitive materials.
For example, when the bleaching step is carried out for photographic color negative photosensitive materials using a bleaching solution of ferric complex salt aminopolycarboxylate, the required bleaching time is at least four minutes and, moreover, complex controls such as pH control of the bleaching solution and aeration are required to maintain the bleaching ability. Even with the sophisticated controls, however, bleaching failure frequently occurs.
In addition, it is necessary that the aforesaid bleaching step be followed by a desilverizing step using a fixing solution and requiring at least three minutes to conduct. Thus, shortening the time required for this step has been strongly desired.
On the other hand German Pat. No. 866,605 discloses a method of speeding up desilverization by using a bleaching-and-fixing solution containing, in a single solution, both the ferric complex salt aminopolycarboxylate and the thiosulfate. In this case, the ferric complex salt aminopolycarboxylate, which has low oxidizing ability (bleaching ability), is mixed with the thiosulfate, which has reducing ability. Thus, the bleaching ability of the former is considerably decreased. Therefore, this bleaching-and-fixing solution is not easily able to desilverize high-sensitivity and high-silver photographic color photosensitive materials, and is not suitable for practical use. Various suggestions have been made regarding improvement of the bleaching-and-fixing solution. These include, for example, a method involving addition of iodides and/or bromides as disclosed in British Pat. No. 926,569 and Japanese Patent Publication No. 53-11854; and a method in which the density of the ferric complex salt aminopolycarboxylate is increased by using triethanolamine as disclosed in Japanese Unexamined Patent Publication No. 48-95834. These methods, however, are insufficient in effect and impractical.
As another method for increasing the bleaching ability of the ferric complex salt aminopolycarboxylate, there has been suggested a method of adding various bleaching accelerators to the bleaching bath and/or the bleaching-and-fixing bath, or the bath preceding these baths.
Among the known bleaching accelerators are included: various mercapto compounds as disclosed in U.S. Pat. No. 3,893,858, British Pat. No. 138,842, and Japanese Unexamined Patent Publication No. 53-141623; compounds containing disulfide bonds as disclosed in Japanese Unexamined Patent Publication No. 53-95630; thiazolidine derivatives as disclosed in Japanese Patent Publication No. 53-9854; isothiourea derivatives as disclosed in Japanese Patent Publication No. 53-94927; thiourea derivatives as disclosed in Japanese Patent Publication No. 49-26586; thioamide compounds as disclosed in Japanese Unexamined Patent Publication No. 49-42349; and dithiocarbamates as disclosed in Japanese Patent Publication No. 55-26506.
Although some of these substances give some measure of bleaching acceleration, the effect is not necessarily sufficient to shorten the required time for processing to the desired degree.
On the other hand, it is well known in the art that the processing method using the bleaching bath and the fixing bath has poor desilverizing ability and does not provide the required rapid processing when the magenta coupler is a 4-equivalent coupler. This disadvantage can be reduced to a certain extent by using a bleaching bath or a bleaching-and-fixing bath to improve the desilverizing ability, but this improvement still does not sufficiently increase the processing speed.